The variability of electronic component characteristics with environmental changes is basic to practical applied electricity. The performance of electrical and electronic circuits depends directly on constituent component characteristics, such as resistance and capacitance, and when these characteristics change as a result of temperature or humidity operation of the parent circuit also changes.
There are many characteristics of electronic components which are commonly of interest to the designer. As an example, a resistor has characteristics such as resistance, tolerance, operating temperature range, power rating versus temperature, inductance, capacitance, temperature coefficient, humidity, aging, and so forth. Capacitors and inductors have similar performance characteristics, as do transistors and diodes and in general every electrical and electronic component.
A common example is a circuit where the frequency or a voltage level may depend on the value of resistance of a specific resistor. If the value of resistance changes the frequency or voltage also changes. This may not be what the designer intends, as in many cases such variability causes unacceptable circuit operation. Attempts to rectify this problem may range from securing if possible a better grade resistor to a complete circuit redesign.